On Dec. 2, 2015, married couple Syed Rizwan Farook and Tashfeen Malik gunned down 22 people and injured 14 at the Inland Regional Center in San Bernardino, Calif.

Officials investigating that case now believe they have discovered a major motive behind the terrorist attack: a mandatory training session in a room filled with holiday decorations, including a Christmas tree.

According to emails obtained by the FBI, Malik was extremely upset that her husband, who worked at the Inland Center, had to go to the festive training session.

“She had essentially made the statement in an online account that she didn’t think that a Muslim should have to participate in a non-Muslim holiday or event,” San Bernardino police chief Jarrod Burguan told ABC News.

“That really is one over the very, very few pieces of potential evidence that we have that we can truly point to and say, ‘That probably is a motive in this case.’”

RELATED: President Obama speaks to those “concerned about terrorism” after San Bernardino shooting

Farook and Malik, who were shot and killed by police four hours after their attack, left behind a 6-month-old daughter. She currently remains in state foster care.

“It certainly surprised me that you’d have a woman with a 6-month old baby who do something like this,” said David Bowdich, head of the FBI Los Angeles office at the time. “That’s very hard for us to comprehend.”

RELATED: The San Bernadino shooting isn’t a good reason to militarize the police

Police officials believe that an extreme hatred for Christmas was the primary motive behind San Bernardino shooting FBI, left, and California Department of Motor Vehicles via AP

Richard Thompson is an associate editor at Rare. Follow him on Twitter @RThompson_91 

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